1. Field of the Invention
The present invention relates to a clutch housing for an automatic transmission used in an automobile or the like, and to a method of manufacturing thereof.
2. Description of the Related Art
Conventionally, a clutch housing has been formed in such a way that a boss portion which requires a stiffness is formed from a billet by forging or cutting while a drum portion is formed into a drum-like shape from a flat plate by pressing or the like, and both portions are thereafter coupled together by plastic deformation or welding.
In order to ensure an appropriate wall thickness for a product so as to satisfy demand characteristics, the clutch housing has been manufactured as a product consisting of not less than two kinds of portions coupled together. In general, portions, that is, the so-called inner hub and outer housing, have been formed under different process controls, have then been coupled by plastic deformation or welding, and have finally been finished.
However, since two portions have been coupled by plastic deformation or welding, there have raised a problem of lowering the strength of a coupling part therebetween or lowering of the reliability thereof, and further, a problem of requiring a contour finishing process of a forged portion formed from a billet with the use of cutting. Further, in a conventional forming process, since an appropriate wall thickness cannot be ensured for demand characteristics in the case of integral formation, separate product designs and separate process plannings have been inevitably required, and accordingly, there has been raised such a problem that hindrance to manufacturing costs due to the necessity of an extra cutting process caused by a material layout in view of a maximum wall thickness, and of a coupling process in view of separate product designs and the like, and a risk of lowering the reliability have not been able to be completely eliminated.
In order to ensure a required strength, Japanese Patent Laid-Open No. H08-309469 discloses a process for restraining roll-over of a corner part of a product. However, in this process, a wall thickness can not be ensured for several parts, except only a part such as a corner part, and accordingly, there has been raised a problem in view of ensuring an overall strength of a hub portion.
Thus, an object of the present invention is to provide a method of manufacturing a clutch housing, in which a boss portion and a drum portion can be integrally formed by pressing, a sufficient wall thickness can be obtained for any of required parts so as to enhance the strength while external dimensions can be substantially finished by press-forming so as to eliminate the necessity of extra process steps and the necessity of an extra contour finishing process step which are caused in the case of coupling two portions, thereby it is possible to reduce the manufacturing costs.